1. Field of the Invention
The application relates to a non-contact magnetic sensor for detecting the open and closed states of a foldable cellular phone, and more particularly, to a magnetic sensor which can suppress irregularity of a central potential due to a change in a temperature, thus decreasing the size and manufacturing cost of the sensor.
2. Description of the Related Art
A method of assembling a magnetic sensor is disclosed in JP-A-2003-066127. According to JP-A-2003-066127, a plurality of magneto-resistive elements are formed on the same substrate. The fixed layers (pinned layer) of all the magneto-resistive elements are magnetized in the same direction, and the substrate is cut out into a plurality of element bases. A combination of the magnetization directions of the fixed layers of the magneto-resistive elements is set with respect to the cut-out element bases, thereby assembling a plurality of element bases together (for example, claim 1 of JP-A-2003-066127).
FIG. 14 is a partial top plan view of the known magnetic sensor. As shown in FIG. 14, the magneto-resistive elements 63 and 64 are provided on the element bases 61 and 62, respectively.
Terminal sections 63a and 64a are provided at both ends of the magneto-resistive elements 63 and 64 in the length directions thereof and each of the terminal sections 63a and 64a is electrically connected to a terminal section 66 on a circuit board 65 by wire bonding, for example.
In the magnetic sensor, for example in order to detect a change in a central potential, the fixed layers in the magneto-resistive elements 63 and 64 are magnetized in directions opposite to each other, as shown in FIG. 14.
The magnetic sensor shown in FIG. 14 is used for detecting the open and closed states of a mobile phone, for example. That is, a magnet is provided on a first member (for example, a member in which a display screen is mounted) of the mobile phone and the magnetic sensor shown in FIG. 14 is incorporated in a second member (for example, an operation member). The magnitude of an exterior magnetic field from the magnet influencing on the magneto-resistive elements 63 and 64 varies between the open and closed states of the mobile phone. Specifically, when the mobile phone gets opened from the closed state, the magnitude of the exterior magnetic field from the magnet influencing the magneto-resistive elements 63 and 64 gradually decreases. In this case, since the resistance values of the magneto-resistive elements 63 and 64 are changed in accordance with a relation between the magnetization directions of the fixed layer and the free layer, the magnetization direction of which varies with the influence of the exterior magnetic field, it is possible to detect the open and closed states of the mobile phone from the change in an output voltage based on the change in the resistance value.
Since the magneto-resistive elements 63 and 64 of which the magnetization directions of the fixed layers are different from each other are used in the known magnetic sensor shown in FIG. 14, it is impossible to form the two magneto-resistive elements 63 and 64 on the same element base. As disclosed in JP-A-2003-066127, the element bases 61 and 62 are cut, and then it is required to match the directions such that the magnetization directions of the fixed layers in the magneto-resistive elements 63 and 64 are opposite with each other.
However, it is considerably difficult to match the directions of the element bases 61 and 62 with high precision, the difficulty has a tendency to bring a fluctuation to the magnetization direction of the fixed layers. This causes irregular detection in the operation of detecting the open and closed states.
Additionally, a combination of a plurality of element bases, as depicted in FIG. 14, makes the magnetic sensor too large. As the number of bonding positions between the terminal sections 63a and 64a of the magneto-resistive elements 63 and 64 and terminal section 66 of the circuit board 65 increases, the manufacturing cost increases accordingly.
Meanwhile, when a bridge circuit is configured by combining the magneto-resistive element with the fixed resistor, for example, the magneto-resistive element and the fixed resistor can be formed on the same element base, thereby solving the above problems.
However, since the materials of the magneto-resistive element and the fixed resistor are different from each other, temperature coefficients of resistance (TCR) thereof are different from each other. As a result, as the temperature varies, a central voltage becomes unbalanced and the detection precision is lowered, thereby causing false operation.